The invention relates to mineral fibre products which have a solubility in biological fluid which is considered to be acceptable but which are durable in use and are based on rock, slag, stone or other mineral melt.
Some mineral fibres are made from vitreous mineral melt, such as of rock, slag or other mineral. The melt is formed by melting in a furnace a mineral composition having the desired analysis. This composition is generally formed by blending rocks or minerals to give the desired analysis.
Although there is no scientific evidence establishing that there is a health risk associated with the manufacture and use of these mineral fibres, commercial interests have led manufacturers to provide mineral fibres that can also be alleged to be of improved biological safety.
This allegation of improved safety is usually made on the basis of in vitro test that examines the dissolution rate or degradability of the fibres in a liquid which is intended to simulate lung fluid, such as Gamble""s solution at about pH 7.5. The test is normally conducted under conditions whereby the fibres are immersed in a previously prepared Gamble""s solution having the specified pH.
Numerous patent applications have been published describing fibres that give enhanced dissolution rate in such an in vitro test, such as WO87/05007, WO89/12032, EP 412,878, EP 459,897, EP 558,548 WO93/22251, WO94/14717 and WO95/21799.
As is apparent from the large amount of literature, of which examples are listed above, directed to the production of fibres which have good solubility as measured by an in vitro pH 7.5 test, a large amount of research has been conducted into optimising the composition of the mineral melt (and the resultant fibres) so as to obtain this high dissolution rate. This optimisation has been applied to the production of fibres that would normally be considered as glass fibres (e.g., in EP 412878) but has especially been applied to the production of fibres which would normally be considered as stone, rock or slag fibres, such as in EP 459878 or EP 558548 or WO95/21799.
The resultant fibres meet the environmental and regulatory desire to provide fibres which, on the basis of an in vitro test, can be shown to be environmentally desirable. An unfortunate consequence is that this research may lead to the production of fibres which fail to provide one of the originally inherent advantages of mineral fibres, namely inertness to ambient humidity. Thus a traditional mineral fibre product is substantially inert to the presence of atmospheric humidity whereas such a product based on cellulosic or other organic fibres may tend to collapse in the presence of atmospheric humidity.
Unfortunately, the mineral fibres which tend to be considered as having good biological solubility (for instance at least 20 and often at least 50 nm/day) have poor resistance to atmospheric humidity, which tends to condense onto the fibres. Thus, the attainment of the allegedly desirable biological solubility is often achieved at the expense of the essential property of inertness to condensed atmospheric humidity.
The condensed humidity may be due to the natural humidity in the atmosphere or the humidity due to wetting of the fibre product by occasional rain or application of cement or other water, especially in enclosed constructions.
There have been proposals to coat stone wool fibres to improve their resistance to hydrolysis in certain environments. For instance, WO94/02427 proposes immersing rock fibres in a composition comprising silane to coat them with silane. No disclosure is given of the particular fibres which are coated, so they would be assumed to be conventional rock fibres having poor solubility in the Gamble""s solution test described above. The exemplified fibres are mixed with an SBR rubber composition to form sealing rings after treatment with silane. Use as a bonded insulation product is not described.
Transferring this knowledge to fibres specifically designed to have good solubility in the Gamble""s solution test would appear to defeat the purpose of conducting the research and development necessary to produce mineral fibres having good solubility in the solubility test using Gamble""s solution. Accordingly, it would appear that the desire for biological solubility is incompatible with the desire for mineral fibres which are relatively unaffected by condensed ambient humidity.
Coating of fibres such as stone wool for other purposes is described for instance in JP-A-2,149,453. Fibres are treated apparently to partially melt the surface by use of a solution comprising aluminium or magnesium by phosphate and a fluoric acid.
Various coatings have also been described for other types of fibre, for instance glass fibre. EP-8-539,342 describes some of these in its background section and also describes a coating composition for glass fibres which comprises aluminium oxide, orthophosphoric acid and water, which form an anionic polymer in situ. The coating is intended to replace the organic resins often coated onto glass fibres to reduce dust and breakage during shipping and handling. WO96/27562 describes coating glass fibres to improve their mechanical strength with weak acids such as boric acid or citric acid or a fatty acid. This binder treating solution can also contain other materials which include ammonium sulphate.
DE 2,556,539 and SE 101,164 also describe glass fibres which are to be used for reinforcement of cement products. The coating is intended to protect the glass fibres from attack by the alkaline environment which prevails in cement products and various alternative coatings are given. These include inorganic acids such as silicic acid and boric acid and organic acids such as oxalic and citric acid, as well as salts of alkali metal, alkaline earth metal and ammonium which include hydrogen phosphate, hydrogen sulphate, hydrogen carbonate, hydrogen borate, hydrogen oxalate, hydrogen citrate and hydrogen tartrate.
These disclosures relate solely to coating of glass fibres which are not designed to be soluble in the Gamble""s solution test above.
The present invention is concerned with the problem of providing mineral fibres traditionally used for their properties of high insulation value and inertness, in particular in forms suitable for use where insulation properties are required. The invention is concerned with the problem of providing fibres which have satisfactory solubility in a biological environment but which do not have severely compromised resistance to atmospheric humidity when in use.
According to a first aspect of the invention we provide a mineral fibre product comprising composite man-made vitreous fibres which have a coating-core configuration wherein the core provides at least 90% by weight of the fibre and is formed of mineral melt formed from components having the following composition, expressed by weight of oxides:
and chosen such that fibres formed from the core alone have a solubility of at least 20 nm/day in Gamble""s solution at pH 7.5 and 37xc2x0 C.
and the coating is coated onto the core and comprises a salt which is a phosphate or hydrogen phosphate of ammonium or quaternary ammonium or alkali metal in an amount of at least 0.3% based on the weight of the core.
Products of the invention containing the defined composite man-made vitreous (MMV) fibres have good ageing resistance when exposed to humidity and/or condensation despite the fact that the majority of the fibre is produced from mineral melt chosen specifically to give a fibre which would be called a xe2x80x9csolublexe2x80x9d fibre without the coating. We find that it is possible to obtain fibres of this type by coating with selected phosphate-containing materials in selected amounts. We find surprisingly that the chosen coating materials give improved ageing resistance in comparison with other materials which might be expected to give equivalent performance. We find also that they do not adversely affect the biological solubility of the fibres as measured in the Gamble""s solution test.
The mineral fibre products of the invention can be used for any of the purposes for which stone, rock or slag wool fibres are known. In particular they are useful in applications where the mineral fibre product is put in position and remains there over a number of months or even years, for instance insulation applications. The product may be used in bonded or unbonded form, but preferably is in bonded form.
According to a preferred second aspect of the invention we provide a rigid bonded mineral fibre product comprising composite man-made vitreous fibres having a coating-core configuration wherein the core provides at least 90% by weight of the fibre and is formed of mineral melt formed of components having the following composition, expressed by weight of oxides:
and chosen such that fibres formed from the core alone have a solubility of at least 20 nm/day in Gamble""s solution at pH 7.5 and 37xc2x0 C.
and the coating is coated onto the core and comprises a salt which is a phosphate or hydrogen phosphate of ammonium or quaternary ammonium or alkali metal in an amount of at least 0.3% based on the weight of the core.
Rigid bonded mineral fibre products have a particular need for ageing resistance but commercially they are desired to show adequate biological solubility. By the invention we can meet both of these needs.
According to a third aspect of the invention we also provide a process for the production of a composite man-made vitreous fibre comprising providing fibres formed from mineral melt and having the following composition, expressed by weight of oxide:
the fibres having a solubility of at least 20 nm/day in Gamble""s solution at pH 7.5 and 37xc2x0 C.,
providing a coating composition which comprises a salt which is a phosphate or hydrogen phosphate of ammonium or quarternary ammonium or alkali metal,
and coating this coating composition onto the fibres in an amount such that the salt is present on the fibres in an amount of at least 0.3% based on the weight of fibres.